This application is a 35 USC 371 of PCT/JP00/00814 filed Feb. 15, 2000.
1. Technical Field
The present invention relates to a wire rod rolling line in which a finishing mill group rear stage is composed of a combination of a plurality of 4-roll mills. In particular, stable operation can be carried out with pinpoint dimensional accuracy by installing 4-roll mills whose motor drive system is improved at the end of the finishing mill group final stage of the wire rod rolling line. Further, a manufacturing efficiency can be improved by simplifying pass schedules as well as a size free range can be expanded and an-equipment cost can be lowered.
2. Description of Related Art
FIG. 1A shows an example of an ordinary wire rod rolling line using 2-roll mills and pass schedules. The wire rod rolling line is composed of a roughing mill group, an intermediate mill group and a finishing mill group,and each mill group has a plurality of mills installed in series. The disposition of the mills in the intermediate and subsequent mill groups is shown on the uppermost row of FIG. 1A. Pass schedules are shown on the second and subsequent rows of FIG. 1A by means of the cross sections of raw materials and products and the roll cavities in respective stands. Note that the roll cavity means the shape of the roll pass of a mill. A billet 1 having a side of 150 mm and an angular cross-section passes through a not shown roughing mill group (first stand-sixth stand). Then, the billet 1 is continuously rolled finally to wire rods 41-49 having a predetermined product size (rod diameter) and a round cross-section by an intermediate mill group 2 composed of a seventh stand 21xe2x80x94a tenth stand 24 and a finishing mill group 3 composed of an eleventh stand 31xe2x80x94an eighteenth stand 38. Note that the stands of odd numbers have vertical rolls assembled therein and the stands of even numbers have horizontal rolls assembled therein. Further, the product sizes are 41: 9.0 mm, 42: 9.3 mm, 43: 9.5 mm, 44: 9.75 mm, 45: 10.0 mm, 46: 10.2 mm, 47: 10.3 mm, 48: 10.5 mm and 49: 11.0 mm. FIG. 1A individually shows pass schedules to obtain wire rods of these products sizes. Oval passes each having an oval roll cavity and round passes each having a round roll cavity are alternately repeated by the 2-roll mills of the respective seventh-eighteenth stands. FIG. 1B is a front elevational view showing the rolling state carried out by the oval pass. Numeral R1 denotes an upper horizontal roll, numeral R2 denotes a lower horizontal roll, and numeral 8 denotes a pass line. Further, FIG. 1C shows the rolling state carried out by a round pass. Numerals R3 and R4 denote right and left vertical rolls numeral 8 denotes a pass line.
All the cavities shown in FIG. 1A have a different size. That is, a dedicated cavity must be prepared for each product size. Thus, each time a product size is changed, the stands must be recombined by stopping a line once. In the case of FIG. 1, nine kinds of products sizes are obtained by preparing nine kinds of lines. To manufacture the nine kinds of the products, the line must be stopped nine times and 76 sets of stands to be recombined are necessary.
In contrast, there has been recently proposed a xe2x80x9csize free rolling technologyxe2x80x9d capable of steplessly manufacturing products of different size with pinpoint dimensional accuracy by using rolls having the same cavity and changing the roll pass of the rolls.
That is, a wire rod rolling technology for installing two 4-roll mills in series with the reducing directions thereof dislocated by 45xc2x0 as the final finishing rolling stands of a wire rod rolling line is disclosed in, for example, Japanese Examined Patent Publication No. 3-6841 and Japanese Unexamined Patent Publication No. 6-63601.
FIG. 2A shows an example of a wire rod rolling line and pass schedules to which the free size rolling technology is applied. The disposition of the mills in the intermediate and subsequent mills in the wire rod rolling line on an uppermost row. The arrangements of the mills of an intermediate mill group 2 and a finishing mill group front stage 3 are similar to those shown in FIG. 1. A finishing mill group rear stage 5 is disposed further downstream of the finishing mill group front stage 3. A finishing mill group is composed of a combination of the finishing mill group front stage 3 and the finishing mill group rear stage 5. The finishing mill group rear stage 5 is composed of the 4-roll mills 51 and 52 of two stands which are installed with the reducing directions thereof dislocated by 45xc2x0. FIG. 2B is a front elevational view showing the rolling state carried out by the 4-roll mill 51 and FIG. 2C is a front elevational view showing the rolling state carried out by the 4-roll mill 52, respectively. Numerals R1-R4 denote rolling rolls and numeral 8 denotes a pass line. Two kinds of pass schedules having a different size free range are shown on the second row and the third row of FIG. 2A by means of roll cavities at the respective stands. A wire rod 61 whose product size is 9.0-10.0 mm can be size-free-rolled by the pass schedule of the second row. A wire rod 62 whose product size is 10.1-11.1 mm can be size-free-rolled by the pass schedule of the third row. Therefore, any optional product size can be obtained which includes the products of the nine sizes of the pass schedules of FIG. 1A when the size is within the range of 9.0-11.1 mm. Moreover, the number of stops of the line which is necessary to change a size is only twice. In addition, the number of stands to be recombined which is necessary to change the size is only 24 stands.
As described above, the range of product sizes which can be manufactured without replacing a cavity can be increased by assembling the two 4-roll mills, which are arranged as one set, to the finishing mill group. Therefore, a line stop time necessary to replace a cavity for the change of a size is shortened, whereby the operating ratio of the line can be increased.
In contrast, when a wire rod is rolled using conventional 2 rolls and 3 rolls, a dedicated cavity must be prepared for each size of wire rods. Therefore, the number of sizes which can be manufactured is limited as well as there is a limit in dimensional accuracy because the wire rod is deformed by the increase of the width thereof.
However, in the example of FIG. 2, each one set of a mill motor (hereinafter, simply referred to as a motor) is disposed to each of the two 4-roll mills used as the final pass and the two 4-roll mills are driven by the different motor, respectively. When the two 4-roll mills each provided with the motor are installed in series, the distance between the stands is restricted as a matter of course because the interference of motor spaces must be avoided. As a result, the following problems are arisen.
(1) The space where the two stands of the final finishing pass cannot help being increased. xe2x86x92 Space saving and the reduction of an equipment cost are difficult.
(2) When the distance between the stands is long, a wire rod is naturally rotated between both the stands. The cross-section of a wire rod having passed through the upstream 4-roll mill is formed to a shape near to approximate square shape. A product having a round cross-section can be obtained by rolling the approximate square shaped material by the downstream 4-roll mill while dislocating the reducing direction of the wire rod by 45xc2x0. The rotation of the angular wire rod must be avoided between both the stands to maintain an accurate reducing direction. Accordingly, expensive guide rollers must be conventionally interposed between both the stands to maintain the attitude of the wire rod so that the angular cross-section thereof is not rotated. xe2x86x92 It is difficult to reduce the equipment cost.
In contrast, when two 4-roll mills are driven by commonly using the one motor, the following problems are arisen.
(3) While the 4-roll mills can steplessly change a rolling size only by changing a roll pass using the same roll cavity (size free rolling), a proper rolling speed must be maintained in accordance with a size. However, when the two 4-roll mills are driven by commonly using the one motor, a size free range is restricted by a rolling speed adjustable range. xe2x86x92 It is difficult to increase a size free rolling possible range.
(4) A rolling speed and necessary torque are greatly different between a large diameter material and a small diameter material. Therefore, to permit a wire rod having a wide range of size to be rolled while driving the two 4-roll mills by the one motor, a motor of large capacity is necessary. xe2x86x92 A cost increase of motor equipment cannot be avoided.
That is, the wire rod rolling line having the 4-roll mill installed only to the final two stages of the finishing mill group has a room for improvement when a drive unit is taken into consideration.
Further, there are conventionally also applied wire rod rolling lines as shown in FIG. 3 or FIG. 4 in which three 4-roll mills are installed in series with the reducing directions thereof alternately dislocated by 45xc2x0 as the final finishing rolling stands of the wire rod rolling lines. The three 4-roll mills are installed downstream of a finishing mill group front stage 3 composed of ordinary 2-roll mills.
Applied to the wire rod rolling line shown in FIG. 3 is a system for driving the three 4-roll mills 71, 72 and 73 by one common motor 9 through one speed increaser 8 (hereinafter, referred to all passes commonly drive system). In contrast, applied to the wire rod rolling line shown in FIG. 4 is a system for independently driving the three 4-roll mills 71, 72 and 73 by combining each ones of all the three speed increasers 81, 82 and 83 and all the three motors 91, 92 and 93 with each of the three 4-roll mills, respectively (hereinafter, referred to all passes independent drive system).
The 4-roll mill can carry out the xe2x80x9csize free rollingxe2x80x9d, by which a rolling size can be steplessly changed, only by changing a roll pass using the same roll cavity. In a wire rod rolling line for continuously rolling a wire rod by installing a plurality of the 4-roll mills in series, it is necessary to balance the mass flows of a material to be rolled on an upstream side and a downstream side by more increasing the circumferential speeds of the rolls of mills which are located at more downstream positions where the cross-sectional area of the material to be rolled is more reduced. The balanced mass flows permit the material to be rolled between the mills without being miss-rolled by buckling or without being torn off.
However, in the all passes commonly drive system of FIG. 3, the circumferential speed ratios of the rolls of the three 4-roll mills are fixed. The cross-sectional areas of roll passes are determined so that (the cross-sectional area of a material to be rolled)xc3x97(roll circumferential speed) is univocally constant, that is, the mass flow is univocally constant, whereby the mass flows in the respective mills are balanced. Accordingly, in FIG. 3, the ratio of the cross-sectional areas of the first 4-roll mill 71 (first pass) and the second 4-roll mill 72 (second pass) and the ratio of the cross-sectional areas of the second 4-roll mill 71 (second pass) and the third 4-roll mill 73 (third pass) cannot be changed. That is, only the area ratio (area reduction ratio of first pass) of the output side material of the finishing mill group front stage 3 just before the finishing mill group rear stage composed of the 4-roll mills and the output side material of the first 4-roll mill 71 can be. changed. However, the maximum area reduction ratio per one pass, that is, the maximum cross-sectional area changeable ratio of the 4-roll mill is about 15% at a maximum. Therefore, the size free range in the case of the wire rod mills of the all passes commonly drive system is limited to about 7-8% of the diameter of a material to be rolled at a maximum.
When the size free range is narrow as described above, the following problems arise because the kinds of necessary roll cavities are increased.
(1) The number of rolling facilities such as mills, rolls and the like in possession is increased and a large space for storing them is necessary, whereby an investment amount is increased.
(2) Since a roll replacing frequency is increased, the operation stop time of a rolling line is increased.
(3) Manpower is necessary in a large amount for grinding of rolls carried out in off-line, setup jobs such as, setting of roll guides to mills, and the like.
Further, when rolling is continuously carried out by the three 4-roll mills driven by the one common motor 9, there is also a problem that a product is made bad when the dimensional accuracy of an input side material is bad because the size of the product is greatly affected by the size of the input side material.
In contrast, in the all passes independent drive system of FIG. 4, the three 4-roll mills 71, 72 and 73 are independently driven by the three motors 91, 92 and 93, respectively. As a result, the cross-sectional area ratio of the material to be rolled at each pass need not be preset different from the all passes commonly drive system. Therefore, a maximum of 15% of the area reduction ratio can be set by both the first pass and the second pass in the 4-roll rolling, respectively. After all, the free size range is doubled to 15% of the diameter of the material to be rolled at a maximum in this case. Note that the third pass of the 4-roll rolling is a final pats for stabilizing the diameter of a product and needs a proper area reduction ratio of about 5%, which does not contribute to the size free range.
However, the all passes independent drive system, which can expand the size free range about twice that of the all passes commonly drive system, also has the following problems.
(1) Since the number of the motors is increased, an investment amount for equipment including the controllers of the motors is increased.
(2) Since the number of revolution of each motor must be set with pinpoint accuracy, operation troubles such as cobbles, tear-off and the like are liable to be caused between the mills.
(3) Since the motors used have a capacity of about 500 KW, the interference between the motors cannot be avoided. Thus, the distance 100 between the first 4-roll mill 71 and the second 4-roll mill 72 cannot help being increased as shown in FIG. 4. When the distance 100 between the mills is increased, the rotation of the material to be rolled is made remarkable between the first 4-roll mill 71 and the second 4-roll mill 72. As a result, miss-rolling caused by the abutment of a material against the guide of a mill and a danger that the dimensional accuracy of a product is lowered are increased.
At present, however, there are required to more expand a size free rolling range in the wire rod rolling as well as to more enhance a manufacturing efficiency and to lower a facility cost.
An object of the present invention is to provide a wire rod rolling line having a very high operating ratio capable of expanding the size free rolling range and at the same time capable of arranging pass schedules in which the pass schedule of an upstream pass is simplified in order to shorten a line stop time.
To achieve the above object, the present invention relating to a wire rod rolling line is characterized in that, in wire rod rolling mills installed in a finishing mill group, the three mills from an end are 4-roll mills, these three mills are installed in series with the reducing directions thereof dislocated by 45xc2x0, the two mills from the end are driven by a common motor and the third 4-roll mill from the end is driven by an independent motor.
The wire rod rolling line of the present invention employs a drive system which makes good use of the advantages of both of an independent motor drive system and a common motor drive system.
That is, the two mills from the end are driven by the common motor and the third 4-roll mill from the end is separately driven. This is for the purpose of preventing the ratio of the cross-sectional areas of materials to be rolled for balancing mass flows in the respective mills from being restricted between a third pass and a fourth pass from the end. Therefore, a maximum of 15% and 15% of an area reduction ratio can be set by both of a third pass and a second pass from the end, respectively. That is, a free size range is expanded to 15% of the diameter of the material to be rolled at a maximum, similarly to the case of the all passes independently driving system shown in FIG. 3.
Moreover, the mill of a final pass, which is a final molding pass and does not contribute to the size free range is commonly driven with the mill of the second pass from the end. As a result, the number of the motor can be reduced as well as the distances between the mills can be shortened similarly to the case of the all passes independent drive. That is, an investment for equipment including motors and their controllers can be reduced by the reduction of the number of the motors. At the same time, the occurrence of miss-rolling due to the rotation of the material to be rolled between the mills and the deterioration of the dimensional accuracy of products can be prevented by the reduction of the distances between the mills.
Further, the 4-roll mill of the third pass from the end may be independently driven or may be commonly driven with a fourth mill from the end. When the mill is commonly driven, the fourth mill from the end is also a 4-roll mill and the third mill and the fourth mill from the end are installed in series with the reducing directions thereof being dislocated by 45xc2x0. Further, it is also preferable that the 4-roll mills are installed so that the output side materials of the final mill and the third mill from the final mill have a round cross-section and that a switching speed increaser dedicated for one of the two mills from the end and a switching speed increaser common to the two mills are interposed between the one of the two mills and a drive motor, the switching speed increaser common to the two mills is interposed between the other mill and the drive motor, and the two mills from the end are coupled with the drive motor.